Oriental Mustard (Sisymbrium orientale) is a dicot weed in the Brassicaceae family. In South Australia this weed first evolved multiple resistance (to 2 herbicide sites of action) in 2005 and infests Cereals. Multiple resistance has evolved to herbicides in the Groups B/2, and O/4. These particular biotypes are known to have resistance to 2,4-D, imazethapyr, MCPA, metosulam, and metsulfuron-methyl and they may be cross-resistant to other herbicides in the Groups B/2, and O/4.

The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

Field, and Greenhouse trials comparing a known susceptible Oriental Mustard biotype with this Oriental Mustard biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetics

Genetic studies on Group B, O/2, 4 resistant Oriental Mustard indicate that the inheritance is determined by a one gene, semi dominant trait. There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature

Mechanism of Resistance

The mechanism of resistance for this biotype is either unknown or has not been entered in the database. If you know anything about the mechanism of resistance for this biotype then please update the database.

Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes. If you have any information pertaining to the fitness of multiple resistant Oriental Mustard from South Australia please update the database.

Postdoctural Fellow/ ConsultantUniversity Of Adelaide - Waite CampusCrc For Australian Weed Management And School Of AgricultureBox 2146Adelaide, 5064, South AustraliaAustralia Email Christopher Preston

ACKNOWLEDGEMENTS

The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in South Australia have been instrumental in providing you this information. Particular thanks is given to Peter Boutsalis, and Christopher Preston for providing detailed information.

A population of oriental mustard from Port Broughton in South Australia was reported as not being controlled by 2,4-D. Dose response experiments determined this population was resistant to both 2,4-D and MCPA, requiring greater than 20 times more herbicide for equivalent control compared to a known susceptible population (from Roseworthy, South Australia) and a population resistant only to the acetohydroxyacid synthase (AHAS)-inhibiting herbicides (from Tumby Bay, South Australia). The Port Broughton population was also found to be resistant to three chemical groups that inhibit AHAS; however, the level of resistance was lower than the known acetolactate synthase-resistant population from Tumby Bay. Herbicides from other modes of action were able to control the Port Broughton population. Assays of isolated AHAS from the Port Broughton population showed high levels of resistance to the sulfonylurea and sulfonamide herbicide groups, but not to the imidazolinone herbicides. A single nucleotide change in the AHAS gene that predicted a Pro to Ser substitution at position 197 in the protein was identified in the Port Broughton population. This population of oriental mustard has evolved multiple resistance to AHAS-inhibiting herbicides (AHAS inhibitors) and auxinic herbicides, through a mutation in AHAS and a second nontarget-site mechanism. Whether the same mechanism provides resistance to both AHAS inhibitors and auxinic herbicides remains to be determined. Multiple resistance to auxinic herbicides and AHAS inhibitors in the Port Broughton population will make control of this population more difficult..

In 2005, failure of 2,4-D to control Sisymbrium orientale was reported in a wheat field near Port Broughton, South Australia, Australia. This paper discusses the resistance of S. orientale to hormone mimic herbicides and AHAS-inhibiting herbicides, and the level of gene flow of the herbicide resistance traits between resistant and susceptible populations..

Three Australian Sisymbrium orientale and one Brassica tournefortii biotypes are resistant to acetolactate synthase (ALS)-inhibiting herbicides due to their possession of an ALS enzyme with decreased sensitivity to these herbicides. Enzyme kinetic studies revealed no interbiotypic differences within species in Km (pyruvate) (the substrate concentration at which the reaction rate is half maximal) but a greater Vmax (the rate when the enzyme is fully saturated with substrate) for two of the resistant S. orientale biotypes over susceptible levels. F1 hybrids from reciprocal crosses between resistant and susceptible biotypes of S. orientale showed an intermediate response to chlorsulfuron compared to the parental plants. ALS herbicide resistance in S. orientale segregated in a 3:1 (resistant:susceptible) ratio in F2 plants with a single rate of chlorsulfuron, indicating that resistance is inherited as a single, incompletely dominant nuclear gene. Two regions of the ALS structural gene known to vary in ALS-resistant biotypes were amplified and sequenced. Resistant S. orientale biotypes NS01 and SS03 contained a single nucleotide substitution in Domain B, predicting a Trp (in susceptible) to Leu (in resistant) amino acid change. Two adjacent nucleotide substitutions (CCT to ATT) predicting a Pro (in susceptible) to Ile (in resistant) change in the primary amino acid sequence were identified in Domain A of resistant S. orientale biotype SS01. Likewise, a single nucleotide substitution at the same site in the resistant B. tournefortii biotype predicts a Pro (in susceptible) to Ala (in resistant) substitution. No other interbiotypic nucleotide differences predicted amino acid changes in the sequenced regions, suggesting that the amino acid substitutions reported above are responsible for resistance to ALS-inhibiting herbicides in the respective biotypes..

It is likely that transgenic canola [rape] expressing genes encoding resistance to glyphosate and glufosinate ammonium will be introduced into the Australian cropping system in the next few years. One risk associated with the introduction of such cultivars is the release of herbicide resistance genes into weedy relatives of canola. This review examines the currently available experimental information regarding the possibility of gene flow from canola to weedy relatives. Three species are identified as having the potential to outcross with canola, Brassica juncea, B. rapa [B. campestris] and Raphanus raphanistrum. The first two of these species are not yet widespread weeds of the southern Australian cropping zone. In contrast, R. raphanistrum is already a major weed in Australia with existing resistance to acetolactate synthase (ALS)-inhibiting herbicides. Information is urgently needed to determine whether successful hybrids between B. napus and R. raphanistrum can be produced under Australian conditions. Major deficiencies in the existing information are identified in relation to some other important weed species within the southern Australian cropping zone. Further studies are required to determine the outcrossing potential of canola to B. tournefortii, Diplotaxis tenuifolia, Sisymbrium officinale and S. orientale if transgenic canola is to be safely and responsibly introduced into Australia..